Exhaust heat exchangers may be advantageously used, for example, to cool exhaust gas, allowing it to be recirculated for emission reduction in vehicles. The recirculated exhaust must be cooled in order to achieve high efficiency during recirculation, especially to achieve better degrees of filling. The entire system (i.e., the vehicle with its internal combustion engine) and an overall significantly reduced energy balance is naturally at issue.
For many years, however, all the operating situations in the vehicle have been analyzed and measures taken according to many different operating situations to be encountered. One such measure consists of bypassing the exhaust heat exchanger in operating situations in which cooling of the exhaust would be counterproductive. Such operating situations include the starting phases of the vehicle, which require considerable fuel and in which the heat energy of the exhaust, for example, may be used directly for rapid warm-up of the engine to its optimum operating temperature. Solutions like those described in European patent applications/patents EP 916 837 and EP 987 427, and ordinarily propose bypassing the exhaust heat exchanger. Specifically, a valve is arranged in front of the exhaust inlet to the exhaust heat exchanger, whereby the valve may feed the exhaust stream, as necessary, through the exhaust heat exchanger or past it directly into the recirculation line. The bypass is integrated in the valve.
Additional solutions have been described in German applications DE 197 33 964 A1 or DE 199 06 401 A1, which show the manner in which recirculation can occur. In the first named document, a bypass line and the exhaust heat exchanger are separated from each other, but both are apparently arranged in a common housing and the bypass line in the latter goes around the heat exchanger outside of it without both being enclosed by a housing. The exhaust heat exchangers themselves are apparently so-called tube bundle heat exchangers or coil tube heat exchangers. These exhaust heat exchangers do not appear to be particularly compact, which is of particular importance in the limited engine compartment space of motor vehicles.
Bypassing the heat exchangers is generally also required in exhaust heat exchangers per se. That is, even in heat exchangers proposed decades ago and (still) used in heaters for the passenger compartments of vehicles, among other things, bypassing is desired because the heat demand is not permanently present. However, those exhaust heat exchangers also usually belong to the tube bundle type or coil tube type. Exhaust heat exchangers, as explained in EP 942 156 A1, are included here.
Integrated bypasses have also been used heretofore, but in connection with heat exchanger designs which often must be manufactured by demanding welding methods, were described in DE 101 42 539 A1, in DE 199 62 863 A1 and in DE 195 40 683 A1.
The present invention is directed toward overcoming one or more of the problems set forth above.